(a) Field of the Invention
The present invention relates to a seven-speed powertrain of an automatic transmission for a vehicle.
(b) Description of the Related Art
A powertrain of an automatic transmission for vehicles has been developed in different ways depending on the vehicle company, and a four-speed or five-speed powertrain is generally used. However, a six-speed automatic transmission has been recently developed and adopted to some vehicles, and a seven-speed automatic transmission is also being developed.
In one example of a seven-speed automatic transmission, a single pinion planetary gear set and one Ravingneaux type compound planetary gear set are combined using three clutches and three brakes to realize seven speeds.
However, although such a powertrain may realize seven forward speeds and one reverse speed, there can be a number of drawbacks. For example, the position of the third brake may hinder a hydraulic line for supplying operating pressure to the first and second clutches. In addition, because the Ravingneaux type compound planetary gear set has a large radial-direction size, such a powertrain has a drawback in drag torque, poor controllability, and a poor durability of the planetary gear because the number of operational elements is great. For the same reason, it has poor productivity and poor design freedom.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person or ordinary skill in the art.